Role of the chemical composition and structure on the electrical properties of a solid state electrolyte: Case of a highly conductive LiPON
Résumé
Lithium Phosphorus Oxynitride glass (LiPON) is the most used electrolyte for lithium solid-state microbatteries. The current main challenge is improving its ionic conductivity without deteriorating its very low electronic conductivity, wide electrochemical window and stability with Li. While the chemical mechanisms of ionic conduction have been intensively studied, they still are controversial and not fully understood to date. Therefore, it is particularly important to well define and understand the influence of the keys parameters acting on the ionic conductivity.
In this study, LiPON is deposited by reactive radio frequency (RF) sputtering of Li$_3$PO$_4$ under nitrogen by two ways. LiPON deposited with a non-standard method exhibits an exceptionally high ionic conductivity (6.7 × 10$^{−6}$ S cm$^{−1}$) compared to the standard method (1.4 × 10$^{−6}$ S cm$^{−1}$). The chemical composition and structure are compared using RBS/NRA and FTIR, respectively. The electrical properties as ionic and electronic conductivities, charge mobility and carrier concentration are measured by impedance spectroscopy. It is demonstrated the positive influence of the disorder created by the phosphate groups on the mobility. This high mobility creates a depletion area at the interfaces which can be suppressed by adding a buffer layer. The interfacial properties are also investigated from both chemical and electrical point of view using ToF-SIMS and impedance spectroscopy.